Many applications require the heating or cooling of an enclosed space for extended periods without breaching the enclosure. For example, a surveillance vehicle may be parked within sight of a surveillance target with the vehicle fully enclosed and any opening of the vehicle would jeopardize the secrecy of the surveillance operations. In these and other applications, the conditioning and cooling of air in confined spaces such as cars and truck cabs and off road machinery cabs has evolved from evaporative coolers to mechanized refrigeration and furnace units. Virtually all of these prior units have required some form of an external power source, such as for example a power take off from the engine operating the vehicle or machine. In the example of the surveillance operation described above, the operation of the engine of the surveillance vehicle would also jeopardize the secrecy of the operation.
Efforts to make the units portable, while emphasizing the need to stabilize the heat exchange medium to avoid sloshing into a servo-mechanical apparatus moving the air, such as that shown and described in Brock, U.S. Pat. No. 5,168,722; have not addressed the problem of running quietly and without exterior detection for a period of many hours without drawing power from the engines of the vehicles in which they are situated. The need to transfer the cooling apparatus from enclosed mobile unit to another in which the user is expected to remain without exiting or being observed for hours at a time requires that the unit fit into a limited space. As the size of the space to be cooled increases, the cooling capacity and efficiency of the cooling unit without corresponding increases in size gains greater importance. Furthermore, such portable units should preferably operate on battery power at low current.
Other units known in the art, while described as portable, are in fact tethered to an exterior source of water or utility power or both. The device disclosed in the Caron, U.S. Pat. No. 5,606,865; as with many such devices claiming portability, must have a continuing source of cool water from a tap and is not useful in a mobile installation or circumstances.
Thus, there remains a need for a system to heat or cool an enclosed space without the need for drawing air or electrical power from out side the enclosed space. The system and method described herein are directed to fulfilling this need in the art.